None.
Not applicable.
Cemented tungsten carbide is a very difficult material to machine. Grinding of round tools, such as drills and end mills is even more demanding as tight tolerances are often required on the finished part. In flute grinding, a specially contoured grinding wheel is used to translate the required shape of the flute to the workpiece. As the wheel wears away during the grinding operation, the size of the flutes cut from the workpiece will change. When this wheel wear becomes excessive, it is necessary to reshape the grinding wheel by dressing. Dressing is counterproductive in that it requires downtime and removal of otherwise useful material from the grinding wheel. A grinding wheel with a higher grinding ratio (defined as volume of workpiece removed per volume of grinding wheel removed) will retain its shape for a longer time, increasing the amount of material that can be removed before the wheel shape deteriorates to the point at which dressing is required. Any improvement that can be made in the number of flutes that can be ground between dressing intervals is directly translated into productivity for the toolmaker. This productivity is realized through less downtime (labor savings) and more finished pieces per grinding wheel (material savings).
Grinding round tools with superabrasive grinding wheels has mainly relied on standard techniques and frequent dressing of the wheel to maintain the desired contours on the finished part. Some operational methods have been patented, such as U.S. Pat. No. 4,186,529 and U.S. Pat. No. 4,115,95, which describe a programmably controlled method for grinding end-cutting tools. This invention utilizes a grinding wheel wear compensation program to compensate for the loss of dimensional tolerance.
A method for applying silver coatings to diamond is described in U.S. Pat. No. 4,403,001. Electroless application of a silver coating to diamond particles, and a composite coating of silver and nickel is described in U.S. Pat. No. 4,521,222. Resin-bonded grinding elements with dual coated diamond grit for dry grinding and wet grinding cemented carbide workpieces. The patents do not report the great benefits achieved with the use of silver-coated abrasives in combination straight oil coolants and low wheel speeds in grinding of round tools, as reported herein.
Resin bond grinding wheels containing silver-coated diamond have shown excellent performance in specific carbide grinding applications. Unexpectedly, it was found that the full benefits of the silver coating are only realized under certain grinding conditions. Thus, flute grinding cemented carbide workpieces with a diamond containing resin bond grinding wheel is improved by restricting the diamond to comprise a silver-coated diamond; conducting the grinding in the presence of a lubricant of only straight oil; and conducting the grinding at a wheel speed of less than about 30 m/s and preferably about 20 m/s. Preferred diamond is coated with about 25% and 75% silver by weight.